Microsoft Releases Fix for IE 5.x Flaw

Microsoft recommends that users immediately install a patch for a flaw in Internet Explorer versions 5.01 and 5.5 that can allow an HTML e-mail to run an executable attachment on a user's computer.

The flaw presents a special danger because it does not require a user to consent to opening an attachment. The user would merely need to open the HTML e-mail.

In addition to sending HTML e-mails, an attacker can exploit the vulnerability by luring users to a Web page on the Internet.

The attachment would be able to take any action that the user is privileged to take on the system, Microsoft says in its description of the vulnerability.

Even if a user is running Outlook or Outlook Exchange, Internet Explorer is used to render HTML e-mails.

Internet Explorer does not handle certain MIME (Multipurpose Internet Mail Extensions) types correctly. With some unusual MIME types, IE executes the MIME instead of prompting the user. An attacker could write an executable and specify that it was one of the unusual MIME types.

The patch eliminates the vulnerability by correcting the table of MIME types and their associated actions in IE.

Internet Explorer 5.01 Service Pack 2, released March 6, is not affected by the vulnerability.